This project really sucks. (Super cheap vac table)

jhitesma · October 22, 2017, 11:38am

Well, I foolishly decided that instead of editing together some existing video of my machine for Ryan’s contest I should start a new project. I’ve been putting off building a vacuum table for awhile but really want one. And since the pink foam I’ve been using as a waste board for my foam board cutting is starting to wear out decided it’s finally time.

Not sure if I’ll actually get the video edited, rendered and uploaded in time…but…here’s a peek at the project anyway:

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It’s really cheap to build, just 3 sheets of dollar tree foam and a 3D printed adapter. I cut the foam with my needle cutter on the MPCNC and all three sheets took about 45 minutes combined. The 3D printed adapter took just over 4 hours…I like cutting things way more than printing them anymore

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Here’s the slightly risque view of it’s exposed bottom. One sheet has vertical 1/4" slots, one has horizontal 1/4" slots and the top has 1/4" holes positioned to align with where the slots line up. The bottom is left open so it can suck itself down to my table.

The slots for the 3D printed nozzle I cut by hand since I couldn’t be bothered to deal with them in CAD. And I wasn’t sure which nozzle I was going to use or if this fancy one would even print. And what a print it was:

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Love watching these “top heavy” prints build…but they do make me nervous! Didn’t even use a brim and it came out first try though. Glad I did the Z mods on my FolgerTech 2020 i3 though since otherwise it wouldn’t have fit…as it was it barely did:

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The last few layers it was pushing my LCD around, and only half of it got any cooling because the wires were dragging on my cooling fan causing it to stop turning for half of each layer.

This crazy 3D printed nozzle is on mobeasts MPCNC low rider inspired foam cutting machine here: Foam Ripper by moebeast - Thingiverse

A simpler option is the nozzle I originally planned on using which I modified from another listing on Thingiverse: Customizable Vacuum Crevice Tip With Offset by jhitesma - Thingiverse it’s a customizer and lets you make your own offset nozzle. But mobeasts was too cool looking for me to not try

It only takes a few minutes to CAD up these sheets…but may as well share my work.

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I did it in OnShape so the link to the project is here: Onshape

Just right click on the 3 different sketches and export them as DXF then CAM up in your usual way. This could be cut with a spindle/router…but for foam I love my needle cutter so of course that’s what I used!

Ok…now back to editing down this video and trying to get it up in time for the contest!

jhitesma · October 24, 2017, 8:16am

I did get the video done…though it ran a little longer than I planned (No thanks to iMovie which kept resetting the machining bits from 200% speed up to 20%) but here’s the whole thing:

If you like it do me a favor and vote for it in Ryan’s contest: https://www.v1engineering.com/forum/topic/10817-contest-submissions/

vicious1 · October 24, 2017, 8:47am

There are only a few votes…Get some family and friends to sign in and vote. Bring in the flight test folks, get them votes!

jeffeb3 · October 24, 2017, 8:59am

Vote early, Vote often, that’s my motto!

jhitesma · October 25, 2017, 10:22pm

I did share it on FT…but not on it’s own post. I should probably do an article over there about it, but a little late for attracting votes now.

Anyway…wanted to update about the vac table. Overall WOW! I can’t believe the difference it’s making in my cut quality. I was super happy with the needle cutter before but now I’m blown away. I didn’t realize how poor my work holding was before just pinning the foam board down in the corners. My cuts are cleaner and my Z is more consistent. There’s still something off with my machine that causes about a 1mm difference in Z from left to right (even though the X and Y rails are level all the way across so it must be something in the gantry rails.) but 1mm of difference over 4’ isn’t keeping me from doing anything I want to do right now.

Now the parts practically fall out of the material when I’m done. Before I’d have to punch them out - didn’t take much effort but they weren’t falling out by themselves. In fact, now if I don’t kind of twist the workpiece as I remove it the parts stay on the vac table (even with the vacuum off.) This could be due to a couple of things that have changed.

First, my waste board is now the same DTFB that I’m cutting not pink foam. So maybe the paper top layer is somehow bonding with my work when the needle goes all the way through. Second my Z is more accurate so I don’t need to penetrate as deep with the needle but I haven’t adjusted my gcode so I’m cutting deeper into the waste board (Before I’d use 6.5mm of cut even though the foam is nominally 4.5mm thick…even then I’d sometimes get areas that it didn’t fully cut due to warps in the foam. Now 5mm cuts always go all the way through but I’m still using 6.5mm cuts out of habit.) Third, my needle is running a little hotter than it was because I bent it when I had the problems cutting the first sheet of the vac table. I straightened it out…but it’s still got a tiny kink in it where it runs in the mig tip of my cutter so that’s causing more friction and heat. So it might be the foam is melting a little and causing it to stick to the waste board.

I don’t mind parts falling out of the stock though - with cuts this clean and the ability to even do 0.5mm “cuts” to add notes and annotations on the pieces (which only pierce the top layer of paper but don’t cut into the foam) I’m super happy:

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What I’m not so happy about is my shop-vac

I just burned out my old original one. Yeah, it’s over 15 years old now (My wife got it for me the first Christmas after we met) and has been making funny noises for awhile…but as I feared drawing this high of a vacuum with a shopvac is apparently not a great idea.

Now…to be fair I probably should have given it a better once over before using it for this…Turns out some of it’s filters have seen better days:

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Didn’t even know that filter was there until I started taking it apart!

From the sounds it was making I thought I lost a bearing…but from the smell it was making I thought I must have burned out a motor winding. Once opened up though I think I know what happened:

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I’m not positive…but I strongly suspect those black bits in there are what’s left of at least one brush. Doubt I can find replacements for it…but I may try and see what I can do. It was still too hot to dig into any deeper though tonight.

I’m hesitant to use my new shopvac I just got for fathers day on it now. It’s bigger and louder for one thing (and that’s the other thing I’m still not big on - the extra noise of running the vac for needle cutting) but it’s also brand stinking new so I don’t want to risk burning it up!

The new vac is a VacMaster vbv1210 and blows away my old 6gallon shopvac brand vac. I think it has separate cooling too…as there are grills on it where it seems to suck in and blow out air separate from the vacuum air. But the exhaust from it does get hotter than I’d like after 15 minutes of running the vac table.

Google gives a lot of mixed info on this application. Some people say they burned out shop vacs almost immediately…others say they’ve been running them in production shops for 4-8 hours a day for 2-4 years with no issues. Probably depends a lot on the style of vac and how much leakage is in the table.

I did remove a bit of foam between two “fingers” of the printed adapter so there’s a gap that lets it bleed some air and get more flow now…but it just made things a LOT louder and the exhaust air still gets warmer than I’d like. But…I see vacuum motors like these: ShopBot Vacuum Motors (which are more than I’d like to spend) which say a 1/4" hole in the plenum provides enough leakage to keep them cool.

I may just look for a cheap shopvac this weekend to dedicate to this and see how it does. I did see that the donek drag knife people use a cheap “$25” shopvac:

And apparently they use that in production work…so I may have to see if I can track one of those down this weekend.

forcerouge · October 25, 2017, 10:39pm

I would say that you need to leave a bit of leakage to the shop vac if you don’t want it to burn.

Reason is that this air is what cools the motor.

Plus, the motor tends to run quite a bit faster at max vacuum, which is bad for your bearings and brushes.

jeffeb3 · October 26, 2017, 5:22am

Hmm. Since your not creating sawdust, you probably don’t need the filter. Makes me wonder if you could get by with an air pump, just joking the intake to the table.

You could add some kind of splitter and valve to adjust the suction to just enough, while allowing as much air as possible to go to the vac.

I would also look for used dust collectors locally on Craigslist or whatever. They will have a motor that’s cooled from ambient air and an impeller to move air. Try to find a small one. They might also be better for constant use than shop vacs.

jhitesma · October 26, 2017, 7:23am

Yeah, that’s why I removed the bit of foam after the old vac burned out. It creates a leakage area to keep some air flowing. But even with that my big vac gets warmer than I’d like it to. Plus that little leakage makes more noise than the vac itself, which is already obnoxiously loud…but the vac I can move out of the shop if I got a longer hose. To move the leak I’d have to add something in the hose…not impossible just more work.

jhitesma · October 26, 2017, 7:33am

I actually took the filter off the little shopvac before doing this…specifically because I figured I didn’t need it and less restriction would be better. I just didn’t realize there was that horrible clogged up filter inside the housing

I actually have a vacuum pump I use for servicing my car/truck AC…but…I don’t know that it’s could pump down this much volume efficiently. I may try it…just going to take more custom fittings than I wanted to deal with to try. It’s actually a little quieter than the shop vac too so it’s got that going for it.

Apparently dust collectors aren’t great for this. The issue is they have lower static pressure and are designed more to move a high volume of air, for a vac table you want the opposite, high static pressure with less volume. But I have seen a few who did get them working.

I suspect the reason a lot of people don’t need to add leakage is that they use porous MDF to build the vac table so they have some “built in” leakage. But a lot of CNC forums also claim that shopvac’s don’t make enough vacuum for “real” CNC work. But I’d say it depends on what you’re doing.

If you’re working on small metal parts you don’t have as much surface area but you need a lot of holding strength so you need higher vacuum. For me working on big sheets of foam…I’ve got tons of surface area and not a lot of force against my work - so I can get by with pretty minimal vacuum.

That said…I do have it sucking itself to the particle board base so I expected there to be some leakage from that. And with the extra leakage hole I added I still can’t move my work and get great cuts. But…it’s definitely not as strong as I can pull the board up to reposition it MUCH easier.

I think I saw those $25 vacs the donek guy uses at wallmart the other day - so I’m going to check that out. I still suspect the big issue is my vac was old and abused and tired. And $25 is cheap enough to almost be disposable if I can get a year or so of use out of it.

I actually also have a blower fan I just took off my car and replaced…before I even started this project I was toying with making a housing for it and seeing if it could create enough static pressure to work. Should be much quieter and it’s got a port that leaks cooling air to the motor. Might be a fun project to try just for kicks. But would increate my 12v load so I’d probably have to add another power supply

jhitesma · October 26, 2017, 8:07am

One more thing I noticed while doing the autopsy on my old shop vac. It didn’t appear to use the vacuum air for cooling. The motor is in a separate compartment, it does have a fan on it as you can see in the photo - but there’s no passage to allow vacuum air to flow through the motor compartment. Instead the motor compartment is ventilated to atmosphere…but it’s not really ducted like my new vac is where it has distinct intake and output ports…it just had a kind of “hat” that sat on some posts and allowed airflow into the motor area.

So…one more sign that it may just have been time for that motor to go.